MDEV-9390 Function found_rows() gives incorrect result where the previous SELECT contains ORDER BY clause

use the raw found_rows value only when SQL_CALC_FOUND_ROWS was specified

Author: vuvova

mysql-test/r/select_found.result

@@ -348,3 +348,18 @@ select found_rows();
 found_rows()
 75
 drop table t1;
+create table t1(c1 int);
+insert into t1 values(1),(2),(3),(4),(5);
+select * from t1 order by c1 limit 2,1;
+c1
+3
+select found_rows();
+found_rows()
+3
+select sql_calc_found_rows * from t1 order by c1 limit 2,1;
+c1
+3
+select found_rows();
+found_rows()
+5
+drop table t1;

mysql-test/t/select_found.test

@@ -277,3 +277,13 @@ select sql_calc_found_rows * from t1 ignore index (i) where i = 0 order by v lim
 select found_rows();
 drop table t1;
 
+#
+# MDEV-9390 Function found_rows() gives incorrect result where the previous SELECT contains ORDER BY clause
+#
+create table t1(c1 int);
+insert into t1 values(1),(2),(3),(4),(5);
+select * from t1 order by c1 limit 2,1;
+select found_rows();
+select sql_calc_found_rows * from t1 order by c1 limit 2,1;
+select found_rows();
+drop table t1;

sql/sql_select.cc

@@ -20813,7 +20813,7 @@ create_sort_index(THD *thd, JOIN *join, ORDER *order,
                             select, filesort_limit, 0,
                             &examined_rows, &found_rows);
   table->sort.found_records= filesort_retval;
-  tab->records= found_rows;                     // For SQL_CALC_ROWS
+  tab->records= join->select_options & OPTION_FOUND_ROWS ? found_rows : filesort_retval;
 
   if (quick_created)
   {